1. Technical Field
Various embodiments of the present disclosure relate to a photomask blank and a method of fabricating a photomask using the photomask blank.
2. Related Art
Highly integrated semiconductor devices exhibit improved operation speed and lower power consumption. Various advanced process technologies have been proposed for reducing the minimum feature size of circuit patterns, such as interconnection patterns, and contact hole patterns employed for electrically connecting the interconnection patterns. For example, various advanced photolithography technologies have been used for forming fine patterns. Generally, photolithography processes employ photomasks, exposure apparatuses and resist materials all of which are important in minimizing the size of the circuit patterns.
Generally, forming accurate photomask patterns on a mask substrate require to accurately pattern a resist layer of a photomask blank. Generally, a phase shift photomask blank may include a phase shifting layer, a light blocking layer and a resist layer which are stacked sequentially on a substrate. Typically, the resist layer is patterned for forming resist patterns, whereas the light blocking and the phase shifting layers are patterned using the resist patterns for forming light blocking patterns and phase shifting patterns, respectively. In such a case, the pitch sizes of the light blocking patterns and the phase shifting patterns are determined by the pitch size of the resist patterns. The resist patterns may act as etch buffers or etch masks while an etch process for patterning the light blocking layer is performed. Thus according to existing processes, the resist layer should be formed to have at least a sufficient thickness for accommodating the above processes. Increasing the thickness of the resist layer generally may improve the accuracy of the light blocking and the phase shifting patterns, however, it may make it more difficult to accurately pattern the resist layer. Accordingly, it is generally difficult to form accurate light blocking and phase shifting patterns.